Overvoltage crowbar and switching power supply circuit

The utility model relates to an overvoltage crowbar for connect in the power, according to mains voltage output overvoltage protection signal. The one end of first resistance, third resistance is connected with the power respectively, the other end of third resistance is connected with the input of switch tube, the output of switch tube is connected with zener diode's positive pole, the base of triode respectively, zener diode's negative pole is connected with the other end of first resistance, and through the 2nd grounding, the collecting electrode of triode with the control end of switch tube is connected, the emitter electrode of the triode is grounded. Third resistance is used for exporting the overvoltage protection signal with the one end that the input of switch tube is connected. Float the coefficient through the thermotropic that utilizes the stabilivolt among the above -mentioned overvoltage crowbar, the subzero temperature that goes to offset between triode base and the projecting pole floats the c